Hi,

Unfortunately, adding categories in the footer a more than just a small modification and is not covered by the free support we offer here. You will have to either search for a third party extension, or seek help in the the official opencart forums.

Here are some topics, you can check:

http://forum.opencart.com/viewtopic.php?t=36953
http://craigmurray.me.uk/opencart-mods/how-to-put-the-category-module-in-the-footer-in-opencart-without-editing-the-source-code/

Best Regards,
ThemeBurn team